#### THE
COLLEGE OF SCIENCE,ZHEJIANG UNIVERSITY

PHYSICS COLLOQUIUM

#### 物理学术前沿讲座

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*A Toy Model for the Pseudogap Phase in Cuprate Superconductors*** **

**by**

**Prof.
Dr. Kun Yang **

**National High Magnetic Field Lab,
USA **

2002年5月10日
星期五16:15-17:15

#### 浙江近代物理中心报告厅
# 203

(light refreshments will be served prior to the
colloquium)

欢迎感兴趣的教师、研究生及高年级本科生参加

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**
ABSTRACT **

In this talk I discuss a simple model we introduced[1] that have a number of
features qualitatively similar to the phenomenology of Cuprate superconductors, especially the existence of a pseudogap region in the phase diagram. In this
model Cooper pairing is induced by an attractive interaction with a finite range. While returning to the usual BCS limit when the range of the pairing

interaction L is shorter than the mean-field coherence length \xi, the physics becomes qualitatively different from that of BCS when L is much larger than
\xi. In this regime the system supports a new class of low-energy collective modes absent in the BCS theory,
whose fluctuations greatly depress the superconducting transition temperature (Tc) from its mean-field level, and

lead to pseudogap behavior above Tc. These fluctuations are not the usual phase fluctuations of the standard superconducting order parameter, and lead
to a highly unusual Ginzburg-Landau description in which the center of mass and relative degrees of freedom of the order parameter must be included on
equal footing. I will discuss how such a long-range pairing interaction may

arise in Cuprate superconductors, especially in the underdoped regime.

[1] Kun Yang and S. L. Sondhi, Phys. Rev. B 62, 11778 (2000).

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